Is my thinking about equivalence right?

Started 3 months ago | Questions thread
bobn2 Forum Pro • Posts: 69,811
Re: Is my thinking about equivalence right?

rogerstpierre wrote:

bobn2 wrote:

rogerstpierre wrote:

Never said that IQ would be similar. I am only saying that there is no correlation between the physical size of the sensor and the size of the rendered image. That is all.

Well, before you were saying that there is no such thing as 'magnification' or 'enlargement' in a digital image. Isn't it very clear that if a lens projects an image which is 17.3 by 13mm and you view it at 173 by 130mm, there is a relationship between those two sizes, like one is ten times the other. Now you decide to view it at 346 x 260mm. The relationship is now that one is 20 times the other. So, let's agree that relationship could be called 'enbigification', however the enbigification happens.

Totally agree on the relationship betwen projected size of the image on the sensor and representational size of the data captured hence a different ratio for a M43 image than a FF one of same resolution.

You see, you start out OK...

It's a relationship to the physical size of the image circle though not a cause and effect as it is for film where a smaller negative must be enlarged more as per your original statement.

Then you veer off again. No. It has nothing to do with the size of the image circle. The lens' image circle might be any size so long as it is large enough to cover the image frame of the camera.

It has to do with the ratio between the physical dimensions of the image frame in the camera, whatever the sensitive medium is, and the physical dimensions of the display frame.

As such, the ratio of projected image to representation will be the same if the larger sensor has a lower resolution equal to that of the ratio between sensor sizes.

The image circle is immaterial. If I buy a Sigma lens for my mFT camera, it will have been designed for APS-C so will have a larger image circle than is needed for the image frame I'm using it with. That doesn't make the degree of enlargement any different from a designed for mFT lens at all when I display or print the result at the size I want to view it.

What you're doing is confusing mechanism and result. With film enlargement occurs optically, using an enlarger to project a bigger image onto another piece of sensitive medium. With digital the process is electronic, performed by resampling from the native pixel array of the sensor to whatever is the required pixel array for the output device or medium at the desired display size. That resampling might happen in a number of different places, such as your image editor or the device drivers for the printer or display, but it will happen. That's the mechanism, not the result. The result is that the image gets enlarged.

Of course, if you use a digital projector, then you're back to optical enlargement fro a part of the process....

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